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Old 16-08-2022, 01:16   #1
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Boiling water efficiently

One of the secrets of managing successfully on solar power is to choose efficient appliances. The aim is to enjoy all the creature comforts without the hassle associated with a generator.

Newer electric kettles have introduced two new technologies that help:

1.They can be selected to stop at a lower temperature than 100C. By stopping just before boiling, the energy wasted converting a liquid into a gas is saved. As a side benefit this also releases much less water vapour reducing condensation and mould problems in the boat.

2. Vacuum insulated kettles are available.

I have used a variable temperature electric kettle for some time, but recently upgraded to newer model with both variable temperature and thermal insulation. The main benefit of the latter is that by retaining heat inside the kettle and in any excess hot water that is not immediately used, there are energy savings on subsequent reboils. This energy saving will depend on the time between reboils and the quantity of water left so quantifing this energy saving in a representative way is difficult.

There are also some energy savings on the first boil. This occurs because less energy is lost via convention while the kettle is heating up. I expected these savings to be quite small, but decided to find out.

I wont bore you with the experimental details, but I tried to control all the variables by using a measured quantity of water and checking the water temperature before and after heating. Results were averaged. Both kettles were set to stop just below boiling (90-95C).

Results:
The non insulated kettle required on average 114 Whrs (this would be about 9.2 Ahrs for a 12v system) to raise 1L (around 1 quart) from around 20C (68F) to just below boiling.
The thermally insulated kettle required 101 Whrs (this would be about (8.1 Ahrs), but actually had a higher finishing temperature (the water was closer to boiling) by around 5C.

After taking the higher finishing temperature into account the vacuum insulated kettle was around 30% more efficient. This is is an impressive result, especially as the savings in subsequent reboils will be much greater.
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Old 16-08-2022, 01:26   #2
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Re: Boiling water efficiently

Another thing is to use the right size of appliance.

We replaced our one liter electric kettle with a 1/2 Liter one.
Perfect for two cups of tea, no unnecessary water is heated.

Since we have enough solar we hardly use the gas hob. One electric plate makes 95% of food we prepare. The Omnia oven works also very well on it.
Just had fresh baked bread from it.

On the odd ocasiones where we need a second plate to heat we use the gas hob.

Our 1300w solar with the 840Ah battery is more than enough, so occasionally we even run the water heater from it or the electric 1000w heater in the bathroom.

Our thermosolar panel provides more then enough temperature to the calorifier on sunny days.

All courtesy of the sun.

We plan to run our small desalinator occasionally as well as soon we finish the installation.

So, yes it's possible to live from renewable comfortably.
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Old 16-08-2022, 03:55   #3
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Re: Boiling water efficiently

ALL for a cup of jo. Not complaint I’m all in. Great idea.
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Old 16-08-2022, 04:03   #4
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Re: Boiling water efficiently

Quote:
Originally Posted by Franziska View Post
Another thing is to use the right size of appliance.

We replaced our one liter electric kettle with a 1/2 Liter one.
Perfect for two cups of tea, no unnecessary water is heated.
.
You do know that you could have simply half filled it

We have a 3 litre kettle but only put in around 800ml (big mugs)
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Old 16-08-2022, 05:22   #5
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Re: Boiling water efficiently

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Originally Posted by Simi 60 View Post
You do know that you could have simply half filled it



We have a 3 litre kettle but only put in around 800ml (big mugs)
Sure, but it was due for replacement anyway and takes up less space
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Old 16-08-2022, 08:32   #6
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Re: Boiling water efficiently

There was a suggestion in this thread:

https://www.cruisersforum.com/forums...-267215-2.html

that boiling water on an induction plate was more efficient than using an electric kettle so I measured ours using the same test. Stopping at the most efficient just below boiling temperature was more difficult with induction, as there is not an setting that will automatically perform this function on my machine, but after a few trials the power consumed was 125 Whrs (or around 10.1 Ahrs). This is the worst performer from an efficiency point of view. In addition, it requires some energy to cool down (the inverter must be left on and there is small fan draw) which was not included in the above.
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Old 16-08-2022, 09:55   #7
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Re: Boiling water efficiently

Sounds like kettle boiling and general cooking need to be segregated when it comes to induction. If you have enough solar the convenience of induction is alluring but requires conductive cookware so all the old pots and pans are replaced. I prefer espresso made Italian style but the bialetti coffeepot is not induction compatible. So I had to get a little plate adapter. Who has room for all this stuff?

Just want to relax and enjoy a coffee for 20 minutes and not think like an engineer but its so hard.
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Old 16-08-2022, 10:28   #8
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Re: Boiling water efficiently

Sounds logical.

With the heating element submerged in the liquid, pretty much 100% of the heat generated by the element is transferred to the liquid. The only losses should be if the container is poorly insulated but with a quick heating process, even poorly insulated, losses should be limited.

With induction, there are multiple energy transitions and at each, there are likely to be losses
- Electricity to magnetic field.
- Magnetic field to heating kettle
- Hot kettle losing heat to the air around kettle

Of course, some of it comes down to how many hot drinks you have per day. We usually do one coffee & tea put in insulated mugs in the morning...saving 1a-hr per day isn't likely to get a lot of attention. If you do tea several times per day, very worthwhile to chase that efficiency.
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Old 16-08-2022, 10:46   #9
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Re: Boiling water efficiently

Quote:
Originally Posted by Sea Beezy View Post
Sounds like kettle boiling and general cooking need to be segregated when it comes to induction. If you have enough solar the convenience of induction is alluring but requires conductive cookware so all the old pots and pans are replaced. I prefer espresso made Italian style but the bialetti coffeepot is not induction compatible. So I had to get a little plate adapter. Who has room for all this stuff?

Just want to relax and enjoy a coffee for 20 minutes and not think like an engineer but its so hard.

I have an induction hob and separate electric kettle which i find works best and is convenient and very quick. Just pop it on top of the gimballed hob when underway to stop it summersaulting across the boat. Easy for coffee, soup, pot noodles (food of champions!) and more. Also means any kettle will do - doesnt have to be for induction.
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Old 16-08-2022, 10:52   #10
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Re: Boiling water efficiently

where did you get your vacuum insulated 12 volt kettle?

The ones I find all have teflon and other toxic coatings.
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Old 16-08-2022, 11:11   #11
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Re: Boiling water efficiently

Quote:
Originally Posted by Sea Beezy View Post
I prefer espresso made Italian style but the bialetti coffeepot is not induction compatible.
https://www.bialetti.com/it_en/moka-induction.html
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Old 16-08-2022, 11:35   #12
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Re: Boiling water efficiently

Quote:
Originally Posted by noelex 77 View Post
One of the secrets of managing successfully on solar power is to choose efficient appliances. The aim is to enjoy all the creature comforts without the hassle associated with a generator.

Newer electric kettles have introduced two new technologies that help:

1.They can be selected to stop at a lower temperature than 100C. By stopping just before boiling, the energy wasted converting a liquid into a gas is saved. As a side benefit this also releases much less water vapour reducing condensation and mould problems in the boat.

2. Vacuum insulated kettles are available.

I have used a variable temperature electric kettle for some time, but recently upgraded to newer model with both variable temperature and thermal insulation. The main benefit of the latter is that by retaining heat inside the kettle and in any excess hot water that is not immediately used, there are energy savings on subsequent reboils. This energy saving will depend on the time between reboils and the quantity of water left so quantifing this energy saving in a representative way is difficult.

There are also some energy savings on the first boil. This occurs because less energy is lost via convention while the kettle is heating up. I expected these savings to be quite small, but decided to find out.

I wont bore you with the experimental details, but I tried to control all the variables by using a measured quantity of water and checking the water temperature before and after heating. Results were averaged. Both kettles were set to stop just below boiling (90-95C).

Results:
The non insulated kettle required on average 114 Whrs (this would be about 9.2 Ahrs for a 12v system) to raise 1L (around 1 quart) from around 20C (68F) to just below boiling.
The thermally insulated kettle required 101 Whrs (this would be about (8.1 Ahrs), but actually had a higher finishing temperature (the water was closer to boiling) by around 5C.

After taking the higher finishing temperature into account the vacuum insulated kettle was around 30% more efficient. This is is an impressive result, especially as the savings in subsequent reboils will be much greater.

How much more power is used with a conventional boil-to-switch-off kettle?
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Old 16-08-2022, 11:57   #13
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Re: Boiling water efficiently

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Originally Posted by Caleb_Grey View Post
Thanks, you're right maybe its time to update. I've got a vintage one passed down through a family.

The underlying theme here is to be adaptable.
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Old 16-08-2022, 13:03   #14
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Re: Boiling water efficiently

Quote:
Originally Posted by noelex 77 View Post
2. Vacuum insulated kettles are available.

I have used a variable temperature electric kettle for some time, but recently upgraded to newer model with both variable temperature and thermal insulation. The main benefit of the latter is that by retaining heat inside the kettle and in any excess hot water that is not immediately used, there are energy savings on subsequent reboils. This energy saving will depend on the time between reboils and the quantity of water left so quantifing this energy saving in a representative way is difficult.
Any heat transferred to anything but the water is considered an energy loss. So even ignoring reboils and even if you only boiled enough water for immediate use, there should be noticeable energy efficiency improvement in an insulated kettle because you didn't have to expend energy to heat up the body of the kettle and the surrounding room.
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Old 17-08-2022, 00:55   #15
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Re: Boiling water efficiently

Quote:
Originally Posted by Simi 60 View Post
You do know that you could have simply half filled it

We have a 3 litre kettle but only put in around 800ml (big mugs)
Absolutely!!

I was looking around for a 500ml kettle but found they were around $60. Two liter kettles are only $17 so now I do as you do and just half fill the kettle
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